Conventional reciprocating piston engines use a crankshaft to convert the reciprocating motion of the pistons to rotating motion of an output shaft. Torque generation in this type of engine is less than optimal as the point of peak pressure in a cylinder (usually shortly after top-dead-center) coincides with a geometry (i.e. an angular relationship) between a connecting rod (connecting the piston to the crankshaft) and the crankshaft that is inefficient for converting the force delivered along the connecting rod to an angular displacement of the crankshaft.
Many commonly used engines such as those typically installed in automobiles and trucks, for example, have the characteristic of generating more torque as engine speed increases, while the loads in these applications would benefit from more torque at low engine speeds. Vehicle manufactures typically employ a gear box (a.k.a. transmission) to enable the generation of more torque at lower engine speeds. The inclusion of the gear box adds to the cost, weight and complexity of the vehicle.
What is needed is a solution that provides significant torque at low engine speeds while mitigating cost, weigh and complexity.